I took a quick look and triggered CI. I had one suggestion but otherwise from my limited knowledge it looked reasonable.
On Tue, Apr 7, 2026 at 8:58 AM Milan Stefanovic < [email protected]> wrote: > Thanks everyone for the review. > > Can some committers review as well, so we can finalize this ? > > Thanks, > Milan > > On Wed, 1 Apr 2026 at 14:26, Milan Stefanovic < > [email protected]> > wrote: > > > Thanks for the explanation Dewey! > > > > I've opened PR: > > https://github.com/apache/parquet-format/pull/560 > > > > Let me know what you think! > > > > P.S. - If you know any relevant party in geo community, lets involve them > > explicitly as well. > > > > cc: @Jia Yu <[email protected]> > > > > Thanks, > > Milan > > > > On Sat, 28 Mar 2026 at 03:32, Dewey Dunnington < > [email protected]> > > wrote: > > > >> Hi Milan, > >> > >> > Dewey, you mentioned current writers using inline strings - what are > >> they > >> > inlining ? are they inlining projjsons or authority:identifiers ? > >> > >> The writers are writing the CRS representation they receive, which for > >> Arrow C++ and arrow-rs comes from the geoarrow.wkb extension type > >> metadata [1]. This is usually PROJJSON but is permitted to be a string > >> (including authority:code). If you run > >> pyarrow.parquet.write_table(pyarrow.table(geopandas_geof.to_arrow())) > >> today, you will get a Parquet file with an inlined PROJJSON CRS, > >> because that is how GeoPandas encodes CRSes when converting to Arrow. > >> > >> > reality of current implementations is such > >> > that most implementations do write `authorithy:identifier`, spec > should > >> be > >> > written so that at least it doesn't look like thats invalid. > >> > >> The reality of current implementations is that they are writing > >> PROJJSON, although I would also happily support a rewording that adds > >> authority:code to the recommended options list. > >> > >> > Arent EPSG:<number> also understood to map directly to > >> > corresponding PROJJSON definition ? > >> > >> They can be mapped to a PROJJSON definition (or a number of other less > >> friendly export formats) using a database with the licensing ambiguity > >> Jia mentioned. Conversely, PROJJSON can be mapped to authority:code > >> with some minimal JSON parsing (we do this in Arrow C++ and arrow-rs > >> to canonically remove CRS definitions that correspond to lon/lat to > >> produce more universally consumable Parquet files). > >> > >> Cheers, > >> > >> -dewey > >> > >> [1] https://geoarrow.org/extension-types.html#extension-metadata > >> > >> On Fri, Mar 27, 2026 at 3:52 PM Milan Stefanovic > >> <[email protected]> wrote: > >> > > >> > Thanks Jia and Dewey, > >> > > >> > Dewey, you mentioned current writers using inline strings - what are > >> they > >> > inlining ? are they inlining projjsons or authority:identifiers ? > >> > Given that current implementations avoided using srid:<number> and > >> > projjson:<field_ref> perhaps we should remove these examples from spec > >> as > >> > they seem to bring some confusion. > >> > > >> > @Jia Yu <[email protected]>, you mentioned that OGC:CRS84 are > >> understood to > >> > map directly to its corresponding PROJJSON definition. > >> > Arent EPSG:<number> also understood to map directly to > >> > corresponding PROJJSON definition ? > >> > > >> > Also I'm fine with not being explicit about `authorithy:identifier` if > >> that > >> > was the prior consensus, but if reality of current implementations is > >> such > >> > that most implementations do write `authorithy:identifier`, spec > should > >> be > >> > written so that at least it doesn't look like thats invalid. > >> > > >> > What are your thoughts? > >> > > >> > Milan > >> > > >> > On Wed, 25 Mar 2026 at 15:53, Dewey Dunnington < > >> [email protected]> > >> > wrote: > >> > > >> > > Hi Milan, > >> > > > >> > > A short answer is that the current language of the spec does not > >> > > forbid writing "OGC:CRS84" to the CRS field (which is "just a > string" > >> > > as far as thrift is concerned). All existing readers that I know > about > >> > > (DuckDB, arrow-rs, Arrow C++, GDAL) will accept that string and > >> > > interpret it unambiguously on read (for example, > >> > > `GeoPandas.from_arrow(pyarrow.parquet.read_table(...))` works). > There > >> > > is also an example file in parquet-testing that covers this case > >> > > (arbitrary string that is neither of the recommended options) [1]. I > >> > > put together a small example script to demonstrate the read path for > >> > > the tools I mentioned [2]. > >> > > > >> > > Jia is correct that the GeoParquet community will require writing an > >> > > inline PROJJSON string in the forthcoming 2.0 version of the > >> > > specification [3]. This was a pragmatic decision that reflects the > >> > > needs of existing GeoParquet users because: > >> > > > >> > > - srid does not explicitly name the EPSG database, so any code > written > >> > > there does not have an unambiguous interpretation (even if it did it > >> > > would place ambiguous licencing and/or dependency requirements on > >> > > consumers) > >> > > - projjson:some_field was not pragmatic to implement on the write > side > >> > > for either of the implementations I was involved in (C++ and Rust). > >> > > Implementations just don't expose the global key/value metadata when > >> > > converting types and doing so would have required breaking changes > in > >> > > the APIs. There are also ambiguities with respect to existing > >> > > propagation of schema metadata (i.e., the projjson schema key is > often > >> > > propagated in unexpected ways into pyarrow and beyond, including > being > >> > > written into the key/value metadata of a resulting Parquet file). > >> > > > >> > > As a result, most of the tools that can write GEOMETRY and GEOGRAPHY > >> > > (Arrow C++, GDAL, arrow-rs are currently writing inline strings > >> > > (because inline strings are what is available in the representation > >> > > passed to Arrow-based writers and this was better than omitting CRS > >> > > information). For all the implementations I was involved in, we also > >> > > try to explicitly omit the CRS when we detect that the string we > were > >> > > passed is lon/lat (i.e., if they see "OGC:CRS84", they write an > >> > > omitted CRS to minimize the need for consumers to be CRS aware). > >> > > > >> > > I'll echo Jia's comment that none of us are keen to reopen a CRS > >> > > discussion but I also agree that the current language of the spec is > >> > > vague and doesn't reflect the reality of the ecosystem as it has > >> > > evolved. I'm happy to review any PRs to improve the language or > >> > > implementations :) > >> > > > >> > > Cheers, > >> > > > >> > > -dewey > >> > > > >> > > [1] > >> > > > >> > https://github.com/apache/parquet-testing/tree/master/data/geospatial#geospatial-test-files > >> > > [2] > >> https://gist.github.com/paleolimbot/7759e58bf1f98ecf8f2c459367bbdeda > >> > > [3] > >> > > > >> > https://github.com/opengeospatial/geoparquet/blob/main/format-specs/geoparquet.md#crs-parquet-property > >> > > > >> > > On Wed, Mar 25, 2026 at 12:49 AM Jia Yu <[email protected]> wrote: > >> > > > > >> > > > Hi Milan, > >> > > > > >> > > > The authority:identifier pattern was explicitly rejected in prior > >> > > > community discussions. The core concern is that it forces query > >> > > > engines to rely on external registries to resolve CRS definitions, > >> > > > which breaks the goal of self-contained data. More importantly, > the > >> > > > most widely used authority, the EPSG database, comes with > licensing > >> > > > terms that are not particularly open-source friendly: > >> > > > https://epsg.org/terms-of-use.html > >> > > > > >> > > > As a result, the community has leaned toward requiring data > writers > >> to > >> > > > use a fully self-contained CRS representation such as PROJJSON. In > >> > > > that model, a reference like OGC:CRS84 is understood to map > directly > >> > > > to its corresponding PROJJSON definition, as outlined in the > >> > > > GeoParquet specification: > >> > > > > >> > > > >> > https://github.com/opengeospatial/geoparquet/blob/main/format-specs/geoparquet.md#ogccrs84-details > >> > > > > >> > > > That said, this expectation is not clearly spelled out in the > >> Parquet > >> > > > and Iceberg specifications, which leaves some ambiguity in > practice. > >> > > > > >> > > > I don’t have a strong stance either way. In fact, I can see the > case > >> > > > for allowing authority:identifier. But it’s worth noting that > >> > > > introducing it now would likely reopen a fairly contentious > >> discussion > >> > > > in the community. > >> > > > > >> > > > Jia > >> > > > > >> > > > On Tue, Mar 24, 2026 at 10:09 AM Milan Stefanovic > >> > > > <[email protected]> wrote: > >> > > > > > >> > > > > Hi everyone, > >> > > > > > >> > > > > I’m looking for some clarification (and potentially a small spec > >> > > update) > >> > > > > regarding the Geospatial Physical Types documentation - > >> > > > > https://parquet.apache.org/docs/file-format/types/geospatial/, > >> > > specifically > >> > > > > the CRS Customization section. > >> > > > > > >> > > > > 1) The Confusion > >> > > > > > >> > > > > Currently, the spec states that custom CRS values should follow > >> the > >> > > > > `type:identifier` format, where type is either `srid` or > >> `projjson` - > >> > > > > (e.g., `srid:4326` or `projjson:property_name`). The spec also > >> defines > >> > > the > >> > > > > default CRS as `OGC:CRS84`. > >> > > > > > >> > > > > Depending on how the specification is read, the reader may > >> consider as > >> > > > > valid CRS definition to be only strings of the form `srid:<some > >> > > number>` or > >> > > > > `projjson:<property name>`, which implies that `OGC:CRS84` does > >> not > >> > > adhere > >> > > > > to the rules defined in the customization section. This creates > >> > > confusion > >> > > > > for implementers: should the type string always be parsed as a > >> strict > >> > > > > "custom" format which necessitates the srid: prefix? > >> > > > > > >> > > > > 2) The Suggestion > >> > > > > > >> > > > > I suggest we update the language to be explicit about allowed > >> formats > >> > > for > >> > > > > CRS, and my suggestion is that we break it down like this: > >> > > > > - Standard CRS: Any string from a known authority in a format > >> of > >> > > > > `<authority>:<identifier>` (e.g., `EPSG:4326`, `OGC:CRS84`, > >> > > `ESRI:102100`) > >> > > > > is accepted. > >> > > > > - Custom CRS: in the format of `type:identifier` > >> > > > > - `srid:1234`: The definition resides in a > local/database > >> > > spatial > >> > > > > reference table. > >> > > > > - `projjson:key`: The definition is stored in Parquet > >> > > file/table > >> > > > > metadata. > >> > > > > > >> > > > > This would validate `OGC:CRS84` as a first-class string while > >> > > providing a > >> > > > > clear "escape hatch" for custom definitions. > >> > > > > > >> > > > > What are your thoughts ? > >> > > > > > >> > > > > Kind regards, > >> > > > > Milan > >> > > > >> > > >
